Effect of Thyroid Hormone Excess and Deficiency on Serum Thyrotropin in Rats Immunized Passively with Antiserum to Somatostatin 1

Summary

Passive immunization or rats with antiserum to somatostatin (anti-SS) caused about a 2-fold increase in the basal serum TSH levels and a 1.5-fold rise in serum TSH after TRH, as compared to rats treated with normal sheep serum (NSS). When the basal and the TRH-stimulated TSH levels were suppressed to about half the control levels with 100 ng of T₃/100 g BW, the neutralization of the endogenous somatostatin secretion with anti-SS significantly increased the basal as well as the post-TRH TSH levels. After administration of 200 ng of T₃/100 g BW, the basal TSH levels in the anti-SS- and NSS-treated animals were the same, but, in response to TRH, the TSH levels rose significantly higher in the anti-SS-treated group. When higher doses of T₃ (1 and 10 μg/100 g BW) were given, anti-SS failed to affect the basal or the post-TRH TSH levels. The elevated TSH levels 1 and 3 days after thyroidectomy were further increased by treatment with anti-SS as compared to NSS. The highly elevated level of TSH on the seventh day after thyroidectomy was, however, not affected by anti-SS. These findings indicate that somatostatin modulates the TSH secretion rate under physiological conditions and can be considered with TRH and thyroid hormones as another regulator of TSH secretion.

The authors would like to express their appreciation for the technical assistance of Mrs. D. Pierson and Mrs. J. Gauthier.